We will continue our studies of the repair of DNA damage induced in normal and diseased human cells by radiation and chemicals. DNA damage induced by radiation: We will concentrate on studies of the repair of near ultraviolet damage in Xeroderma pigmentosum cells and Fanconi's Anemia cells. We will also continue our attempts to characterize on a molecular level the excision deficiency for gamma-ray lesions of the 5,6-dihydroxy-dihydrothymine type which we have discovered in two Fanconi's Anemia lines. DNA damage induced by chemicals: We will continue our studies of the repair of DNA damage induced in alveolar tumor cells by the polycyclic aromatic hydrocarbon carcinogen benzo(a)pyrene. Studies of the excision of covalent benzo(a)pyrene-adducts from DNA will complemented with studies of the completion of parent strand repair and the effects of the damage on daughter strand synthesis. The characteristics of benzo(a)pyrene repair will be compared to the repair of DNA lesions induced by N-acetoxy-acetylaminofluorene and ethylnitrosourea.